Prolog/Definite Clause Grammars

Prolog has a mechanism for defining certain grammars called Definite Clause Grammar notation. This makes it easy to write parsers. Note that while DCG syntax is part of the ISO standard, DCG semantics are not.[citation needed]

It means, that the sentence clause will receive L0 as input, and after parsing from a sentence from L0, it will give back LREMAINDER. Let's assume that your start symbol is sentence. Then LREMAINDER is expected to be [ ] after a succesful parsing. The interpretation of the body of this clause is: if we parse a noun_phrase and a verb_phrase from our sentence, we will get back an empty list.